1) Field of the Invention
The present invention relates generally to cotton harvesters and, more specifically, to flow sensors for detecting blockages in the cotton conveying system of a cotton harvester.
2) Related Art
A typical cotton harvester includes a pair of upright spindle drums which remove cotton from the plants and upright doffer assemblies which doff the cotton from the spindles and direct it through discharge openings into upright discharge structure on the cotton harvester row unit. The cotton is removed from the discharge structure by cotton conveying ducts which carry air jet nozzles to propel the cotton into the basket on the harvester. Cotton and debris can often build up in an area of the cotton conveying system, and it is necessary to detect such a blockage early to avoid crop loss and harvester damage. Once started, a blockage in the area can build up to completely cut off the cotton path within a few seconds. The blockage will cause cotton to wrap around the drum, and a very time consuming row unit cleanout procedure is required before harvesting can continue.
The blockage problem is particularly acute in narrow row cotton harvesters having relatively limited space for the conveying path. For example, in cotton pickers with tandem drum units such as shown in U.S. Pat. No. 4,821,497, a narrow area behind the forward drum is one of the areas most likely to plug.
Various types of detecting systems have been used in the past, including some with air pressure switches such as shown in U.S. Pat. Nos. 3,863,428 and 4,286,424. However, in certain situations such as where the plugging occurs near the discharge structure ahead of the pressure switch, the switch will not function to provide the necessary warning signal to the operator. Therefore, systems with pressure sensors often let certain types of blockages go undetected. Photoelectric cell systems are also available, but the cells are subject to being rendered inoperative by dirt and staining from the cotton material. Therefore, these systems require a high degree of maintenance. Thermistors and thermocouples to sense air flow in a duct, such as shown in U.S. Pat. No. 4,068,223, are available but are also quite sensitive and require relatively complex circuitry which must be carefully calibrated.